Gas generator

ABSTRACT

A gas generator for air bags having a container holding a combustible gas mixture and fitted with a closure which opens into a combustion chamber fitted with a gas outlet in which the gas mixture is ignited by an ignition device. To provide a fast-reacting ignition device and generate a controllable flow of pressurized gas at a relatively low temperature, the container is mainly filled with a pressurized inert gas and contains 0.1 to 2.0% vol. of a hydrocarbon and 0.5 to 10% vol. of a gaseous oxidizing agent. On being actuated, the ignition device opens the container closure, ignites the gas mixture flowing into the combustion chamber and maintains combustion by the continuous supply of energy.

BACKGROUND OF THE INVENTION

The invention refers to a gas generator, preferably for an inflatableairbag for the protection of vehicle occupants, consisting of acontainer holding a combustible gas mixture and provided with a closurewhich opens into a combustion chamber provided with a as outlet in whichthe gas mixture is ignited by an ignition device.

In a gas generator of said kind which is known from DE 41 35 776 C1, thecontainer contains a liquid gas consisting of a mixture of one orseveral short-chain hydrocarbons and dinitrogen monoxide as an oxidizingagent, which is injected into the combustion chamber after theinitiation of the gas generator and is ignited therein by an ignitiondevice with an ignition charge. Thereby the ignition clouds and the hotcombustion gases ignite the liquid gas which vaporizes and volatilizesdue to the occurring expansion in the combustion chamber. In the knowngas generator, the ignited gas mixture shows an explosion-like reactionso that gas pressure peaks destroying the combustion chamber may occur.Thus, in order to reduce the high reaction velocity, in the known gasgenerator an inert gas of carbon dioxide and/or xenon is added to thegas mixture in an amount of preferably 10 through 80% in weight.

The known gas generator is not only detrimental because of the highreaction velocity which is only mitigated by the addition of inert gas,but also because of the use of liquid gas which has to evaporate priorto its ignition so that the supply of additional energy is necessesary.Said evaporation is time-consuming. Furthermore, the high concentrationof fuel gas results in a very high temperature of the combustion gases,which is an additional risk if leaks should occur.

SUMMARY OF THE INVENTION

Consequently, it is the object of the invention to provide a gasgenerator of the kind mentioned at the beginning which, after theinitiation of the ignition device, shows a fast reaction, generates acontrollable flow of pressurized gas at a relatively low temperature andalso is completely safe.

In order to obtain an even better and more efficient combustion, acatalytic coating (for instance Pt or Rh) can be provided at sections ofthe combustion chamber.

According to the invention, said problem is solved by the fact that thecontainer is mainly filled with a pressurized inert gas and contains 0.1to 5.0% vol. of a gaseous fuel and 0.5 through 20% vol. of a gaseousoxidizing agent, and that the ignition device, on being actuated, opensthe container closure, ignites the gas flowing into the combustionchamber and maintains combustion by a continuous supply of energy. Theupper limit values are chosen so that at no time an explosive mixture isobtained.

Due to the low concentration of the amounts of combustible gas andgaseous oxidizing agent in the total mixture of gases, the combustion ofthe gas mixture flowing into the combustion chamber is not automaticallymaintained after the initiating ignition so that the ignition device hasto maintain the combustion of the gas mixture in the combustion chamber.Nevertheless, the inventive gas generator generates a gas flow with therequired flow rate, as the gas flowing into the combustion chamber isignited immediately and needs not to be evaporated first, in order toform an ignitable mixture. Due to the high amount of inert gas in thegas mixture and due to the use of a catalyst, the temperature of thecombustion gas can be kept low, for instance in the range of 400° C. orless.

According to a preferred embodiment it is provided that at least half ofthe gaseous fuel is hydrocarbon or hydrogen. The combustible gas mayconsist of CH₄, C₂H₆, C₃H₈, C₂H₁₀, or H₂ or of a mixture thereof, butpreferably consists of CH₄ or C₃H₈.

The gaseous oxidizing agent advantageously consists of O₂, N₂O or H₂O₂.

Advantageously, the oxidizing agent is O₂.

The inert gas preferably is Ar, but also N₂ may be used.

According to a particularly favorable embodiment it is provided that thegaseous fuel contains 0 through 70% vol., preferably approximately 50%vol., of saturated hydrocarbon, and in addition an unsaturatedhydrocarbon, for instance C₂H₂ or C₂H₄.

The addition of unsaturated hydrocarbons results in a better ignition ofthe gas mixture so that it is used for the initiation and theacceleration of the combustion of the gas mixture which contains alkanesand oxidizing agents.

Advantageously, the pressure of the gas mixture in the container amountsto 100 through 300 bar and preferably to approximately 180 through 280bar.

The ignition device may consist of a solid or liquid pyrotechnic chargearranged externally of the container.

As an ignition device also a laser can be used.

BRIEF DESCRIPTION OF THE DRAWING

One embodiment of the invention is explained in detail in the followingby means of the drawing, the sole FIGURE of which is a sectional viewthrough the gas generator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The gas generator consists of a bell-shaped housing part 1 which, at itsupper end, is provided with an opening 2 closed by a sealing disk 3. Theedge of a pressure container 4 is bonded through welding with thebell-shaped housing part 1 such that the center line of the opening 2coincides with the center line 5 of the pressure container.

In the bell-shaped housing part 1 there are held parts 6, 7 the centerpart 6 of which has a cylindrical chamber 8 which is used foraccommodating a pyrotechnic charge. The chamber 8 is connected with thecombustion chamber 10 via a bore 9 in its top wall. The combustionchamber 10 is closed by an angular closure element from which the upperleg 11 extends in parallel to the top wall of the bell-shaped housingpart 1 being provided with the bore 2 and supports the sealing disk 3 inthe inactive state. By means of a nose, the other leg 12 of the closureelement comes into engagement with an undercut of the insert part 6, sothat the closure element is locked in the represented inactive positionin its closing position.

The insert part 6, in its shown position, is locked by the insert part7. The insert parts 6 and 7 are positively locked with the bell-shapedhousing part, wherein a tongue 13 may be bent inwards from the casing ofthe bell-shaped housing part 1 for fixing and locking purposes.

At its upper end, the pressure container 4 is provided with a threadedpin 16 for its fastening and with an opening 17 which is closed by ascrew plug 18 and through which it may be filed.

The pressure container 4 preferably has a volume of approximately 350cm³ and is filled with a gas mixture which may be under a pressure of180 through 280 bar (usually appromixately 230 bar).

In the chamber 8 there may be disposed for instance a pyrotechnic chargeof 3-8 g, depending upon the gas mixture, which may consist of a solidor a liquid. The pyrotechnic charge contains a combustible substance andan oxidizing agent which preferably have a stoichiometric ratio, and mayhave a combustion period corresponding to the discharge period of thecontainer.

The pyrotechnic charge may for instance be ignited by an electricignition device.

When the pyrotechnic charge is ignited, the combustion gases enter thecombustion chamber 10 through the bore 9 so that due to the pressurebeing created in the combustion chamber 10 the leg 12 is pivoted to theleft by releasing Its locking and thereby releases the opening 2. Duringthe flowing-in of the gas mixture into the combustion chamber 10 thepyrotechnic charge maintains the combustion process. The combustiongases; exit through the bore 14 in the bell-shaped housing part 1 andtherefrom for instance flow into an inflatable airbag.

In stead of a pyrotechnic charge, the chamber 8 may also accommodate alaser which then initiates and maintains the ignition.

The openings or bores 14 in the bell-shaped housing part 1 are closed bya network 15 in the shown manner, which consists of a woven wire clothmade of Pt or Rh or of wires with the respective mesh width, which arecoated with Pt or Rh. The network 5 is of an annular shape.

What is claimed is:
 1. A gas generator, preferably for an inflatableairbag for the protection of vehicle occupants comprising a container(4) holding a combustible gas mixture and provided with a closure (3,11) which opens into a combustion chamber (10) provided with a gasoutlet (14) in which the gas mixture is ignited by an ignition device,characterized in that the container (4) is mainly filled withpressurized inert gas and contains 0.1 to 5.0% vol. of gaseous fuel and0.5 to 20% vol. of a gaseous oxidizing agent, the ignition device, onbeing actuated, opens the contained closure (11), ignites the gasmixture flowing into the combustion chamber (10), and maintainscombustions by a continuous supply of energy and continuous ignitionwithin said combustion chamber (10), and concentration of said gaseousfuel and oxidizing agent is, at all times, below an explosive level insaid container (4).
 2. The gas generator according to claim 1,characterized in that the gaseous fuel amounts to 0.2 to 0.5% vol. andthe amount of the gaseous oxidizing agent amounts to 1 to 3% vol. of thegas mixture.
 3. The gas generator according to claim 1, characterized inthat at least half of the gaseous fuel is a gaseous alkane.
 4. The gasgenerator according to claims 3, characterized in that the alkane isCH₄, C₂H₆, C₃H₈ or C₄H₁₀.
 5. The gas generator according to claim 4,characterized in that the alkane is C₃H₈.
 6. The gas generator accordingto claims 1, characterized in that the gaseous oxidizing agent is O₂,N₂O or H₂O₂.
 7. The gas generator according to claim 6, characterized inthat the oxidizing agent is O₂.
 8. The gas generator according to anyone of claims 1, characterized in that the inert gas is Ar.
 9. The gasgenerator according to claim 1, characterized in that the gaseous fuelcontains 0 to 70% vol. of hydrocarbon, and in addition an unsaturatedhydrocarbon.
 10. The gas generator according to claim 9, characterizedin that the unsaturated hydrocarbon is C₂H₂.
 11. The gas generatoraccording to claim 1, characterized in that the gas mixture in thecontainer is subject to a pressure of 100 through 300 bar.
 12. The gasgenerator according to claim 11, characterized in that the gas mixturein the container is subject to a pressure of 180 through 280 bar. 13.The gas generator according to claim 1, characterized in that theignition device is a pyrotechnic charge consisting of a solid or aliquid.
 14. The gas generator according to claim 1, characterized inthat the ignition device is a laser.
 15. The gas generator according toclaim 1, characterized in that, apart from fuel, the container alsocomprises air.
 16. The gas generator according to claim 1, characterizedin that the combustion chamber (10) has outlets (14) which are coveredby a porous structure, as e.g. a network (15) and that this structurecomprises a catalytic substance.
 17. The gas generator according toclaim 16, comprising a catalytic coating of Pt or Rh.
 18. The gasgenerator according to claim 1, wherein temperature of combustion gas ismaintained in the range of 400° C. or less.
 19. The gas generatoraccording to claim 1, structured and arranged such that combustion ofgas mixture flowing into the combustion chamber (10) is notautomatically maintained after initiating ignition, such that theignition device must maintain combustion of the gas mixture in thecombustion chamber (10) while, at the same time, gas flow into thecombustion chamber (10) is maintained at a required rate and the gasflowing into the combustion chamber (10) is ignited immediately withoutevaporation.
 20. The gas generator according to claim 18, structured andarranged such that combustion of gas mixture flowing into the combustionchamber (10) is not automatically maintained after initiating ignition,such that the ignition device must maintain combustion of the gasmixture in the combustion chamber (10) while, at the same time, gas flowinto the combustion chamber (10) is maintained at a required flow rateand the gas flowing into the combustion chamber (10) is ignitedimmediately without evaporation.
 21. The gas generator according toclaim 9, wherein the gaseous fuel contains approximately 50% vol. ofhydrocarbon, and additionally C₂H₂ or C₂H₄.
 22. The gas generatoraccording to claim 3 wherein the pyrotechnic charge is a mixture of fueland oxidizing agents in a stoichiometric relation.
 23. A gas generator,preferably for an inflatable airbag for the protection of vehicleoccupants, comprising a container (4) holding a combustible gas mixtureand provided with a closure (3,11) which opens into a combustion chamber(10) provided with a gas outlet (14) in which the gas mixture is ignitedby an ignition device, characterized in that the container (4) is mainlyfilled with pressurized inert gas and contains 0.1 to 5.0% vol. of agaseous fuel and 0.5 to 20% vol. of a gaseous oxidizing agent, theignition device, on being actuated, opens the container closure (11),ignites the gas mixture flowing into the combustion chamber, andmaintains combustion by a continuous supply of energy, and the containerclosure is constituted by an angular closure element comprising an upperleg (11) of the angular closure element and which is structured andarranged to be pivoted into its open position after the ignition of thepyrotechnic charge acting upon another leg (12) of the angular closureelement.